1. Field of the Invention
Embodiments of the invention relate to a semiconductor memory device data coding method. More particularly, embodiments of the invention relate to a data coding method in an initial operation of a semiconductor memory device.
2. Discussion of Related Art
FIG. 1 is a circuit diagram of a conventional semiconductor memory device 100 to illustrate the transmission and reception of data. FIG. 2 is a graph illustrating an initial operation of the semiconductor memory device 100. Data output through data input/output pads DQ_0 through DQ_n-1 of semiconductor memory device 100 is transmitted to receiving stage RX via transmission stage TX. Transmission stage TX requires a driving current in order to transmit the data to receiving stage RX. When semiconductor memory device 100 outputs ten data bits in a first logic state corresponding to a logic high in an initial operation as illustrated in FIG. 2, the inductance of an inductor connected between a source of power supply voltage VDD and a source of ground voltage VSS is 1 nH. The driving current of transmission stage TX outputting the data bits is 20 mA. The time required to change the logic state of the output data bits to the first logic state is 0.5 ns. The voltage applied to the inductor is represented as:V=n*L(di/dt)=10*1nH*(20 mA/0.5 ns)=0.4V  (1)where n is the number of data bits in the first logic state. That is, the voltage applied to the inductor is 0.4V when ten data bits in the first logic state are output. Accordingly, the voltage drop due to the inductor becomes problematic when the power supply voltage VDD is low while the voltage drop due to the inductor when the power supply voltage VDD is high can be ignored. When the voltage drop due to the inductor is large, data bits that must be output in the first logic state may be output in a second logic state. The second logic state corresponds to a logic low. For example, when the power supply voltage VDD is 1.3V and 1V is required for the output of data bits having the first logic state, the voltage drop caused by the inductor, 0.4V, decreases the power supply voltage VDD to 0.9V. Thus, the data bits outputted cannot be in the first logic state. Accordingly, the logic state of initial data is varied due to the voltage drop caused by the inductor in the initial operation of conventional memory device 100.